The clarity of ultrasound acquired images is affected by motions of the examined subject, the motions of organs and fluids within the examined subject, the motion of the probing ultrasound transceiver, the coupling medium used transceiver and the examined subject, and the algorithms used for image processing. As regards image processing frequency domain approaches have been utilized in the literature including using Wiener filters that is implemented in the frequency domain and assumes that the point spread function (PSF) is fixed and known. This assumption conflicts with the observation that the received ultrasound signals are usually non-stationary and depth-dependent. Since the algorithm is implemented in the frequency domain, the error introduced in PSF will leak across the spatial domain. As a result, the performance of Wiener filtering is not ideal.
As regards prior uses of coupling mediums, the most common container for dispensing ultrasound coupling gel is an 8 oz. plastic squeeze bottle with an open, tapered tip. The tapered tip bottle is inexpensive and easy to refill from a larger reservoir in the form of a bag or pump-type and dispenses gel in a controlled manner. Other embodiments include the Sontac® ultrasound gel pad available from Verathon™ Medical, Bothell, Wash., USA is a pre-packaged, circular pad of moist, flexible coupling gel 2.5 inches in diameter and 0.06 inches thick and is advantageously used with the BladderScan devices. The Sontac pad is simple to apply and to remove, and provides adequate coupling for a one-position ultrasound scan in most cases. Yet others include the Aquaflex® gel pads perform in a similar manner to Sontac pads, but are larger and thicker (2 cm thick×9 cm diameter), and traditionally used for therapeutic ultrasound or where some distance between the probe and the skin surface (“stand-off”) must be maintained.
The main purpose of an ultrasonic coupling medium is to provide an air-free interface between an ultrasound transducer and the body surface. Gels are used as coupling media since they are moist and deformable, but not runny: they wet both the transducer and the body surface, but stay where they are applied. The most common delivery method for ultrasonic coupling gel, the plastic squeeze bottle, has several disadvantages. First, if the bottle has been stored upright the gel will fall to the bottom of the bottle, and vigorous shaking is required to get the gel back to the bottle tip, especially if the gel is cold. This motion can be particularly irritating to sonographers, who routinely suffer from wrist and arm pain from ultrasound scanning. Second, the bottle tip is a two-way valve: squeezing the bottle releases gel at the tip, but releasing the bottle sucks air back into the bottle and into the gel. The presence of air bubbles in the gel may detract from its performance as a coupling medium. Third, there is no standard application amount: inexperienced users such as Diagnostic Ultrasound customers have to make an educated guess about how much gel to use. Fourth, when the squeeze bottle is nearly empty it is next to impossible to coax the final 5-10% of gel into the bottle's tip for dispensing. Finally, although refilling the bottle from a central source is not a particularly difficult task, it is non-sterile and potentially messy.
Sontac pads and other solid gel coupling pads are simpler to use than gel: the user does not have to guess at an appropriate application amount, the pad is sterile, and it can be simply lifted off the patient and disposed of after use. However, pads do not mold to the skin or transducer surface as well as the more liquefied coupling gels and therefore may not provide ideal coupling when used alone, especially on dry, hairy, curved, or wrinkled surfaces. Sontac pads suffer from the additional disadvantage that they are thin and easily damaged by moderate pressure from the ultrasound transducer. (See Bishop S, Draper D O, Knight K L, Feland J B, Eggett D. “Human tissue-temperature rise during ultrasound treatments with the Aquaflex gel pad.” Journal of Athletic Training 39(2):126-131, 2004).
Relating to cannula insertion, unsuccessful insertion and/or removal of a cannula, a needle, or other similar devices into vascular tissue may cause vascular wall damage that may lead to serious complications or even death. Image guided placement of a cannula or needle into the vascular tissue reduces the risk of injury and increases the confidence of healthcare providers in using the foregoing devices. Current image guided placement methods generally use a guidance system for holding specific cannula or needle sizes. The motion and force required to disengage the cannula from the guidance system may, however, contribute to a vessel wall injury, which may result in extravasation. Complications arising from extravasation resulting in morbidity are well documented. Therefore, there is a need for image guided placement of a cannula or needle into vascular tissue while still allowing a health care practitioner to use standard “free” insertion procedures that do not require a guidance system to hold the cannula or needle.